Conventionally, a type of an actuator has been known which driving sprockets engaged with interlocking chains are rotated to thereby drive paired interlocking chains for forward and backward movements (see Patent Document 1, for example).
In the above-described interlocking chain type lift device, as shown in FIG. 13, slipping out of the chains, in which the interlocking chains 250 slip out of a chain guide 272 after ends of the interlocking chains 250 pass through sprocket teeth of a driving sprocket 240, may occur. Therefore a control means that refers to positional information output from a position sensor for detecting the positions of the interlocking chains 250 is provided to electrically or mechanically control the rotation speed of a chain driving motor.